Modification mechanism of green polyurethane modified asphalt prepared by in-situ polymerization

In order to investigate the modification mechanism of green polyurethane (PU) modified asphalt prepared by insitu polymerization, PU was separated from PU modified asphalt (PUMA) and the molecular fragmentation information of synthesized PU and separated PU was characterized by pyrolysis-gas chromatography-mass spectrometry. The binding forms of the asphalt molecules to the PU were deduced, and the deduced structures were validated by infrared spectroscopy, nuclear magnetic hydrogen spectroscopy, gel chromatography, elemental analysis, and molecular dynamics simulation. The results showed that compared to synthetic PU, the PU molecular fragments separated from modified asphalt additionally contained active asphalt components. Meanwhile, infrared and hydrogen spectra verified that the active components in the asphalt can chemically with -NCO in the PU prepolymer. The extension of curing time led to more combinations of asphalt molecules and PU prepolymers, which were manifested in the increases of the element contents of C, O, and S and the increase of molecular weight of PU separated from PUMA. The chain extender could not be completely reacted during the preparation and curing of PUMA and after curing for 6 months, the binding rate of PU prepolymer and chain extender was 24.80 %. PU prepolymer can react with the moisture in the air to generate amine group, and further generates urea group during the preparation and curing of PUMA. This work serves as a reference for the design and preparation of PUMA by in-situ polymerization.